Project Summary/ Abstract The long-term objective of these studies is to understand interactions between androgens and progestins in regulating catecholaminergic neurons. Circulating androgen levels are low in females, but change during the reproductive cycle and play important physiological roles. Progesterone has important functions during the reproductive cycle and is essential in pregnancy maintenance in mammals. Females can exhibit elevated androgen levels in reproductive and metabolic disorders, such as polycystic ovary syndrome. Some of the most commonly used hormonal contraceptives contain progestin compounds, which also exhibit androgenic activities. Thus, there may be times when androgens and progesterone are circulating together at levels sufficient to activate their respective receptors at the same time. Our laboratory has identified a unique interaction of testosterone-bound androgen receptor (AR) and progesterone-bound progesterone receptor (PR) within a steroid responsive region of the tyrosine hydroxylase (TH) promoter. TH is the rate-limiting enzyme in dopamine and norepinephrine biosynthesis. The overall objective of this study is to put molecular interactions of androgens and progesterone into a physiological context in the regulation of TH gene expression. We propose to examine AR and PR effects on TH gene expression in the brains of female rats. The hypothesis for this study is that subpopulations of catecholaminergic neurons express both AR and PR in the same cell and that progesterone and androgens interact to augment TH mRNA expression is brain regions with AR and PR co-localization. Aim 1 is to evaluate the localization of AR and PR in catecholaminergic neuronal groups in the hypothalamus, midbrain and brainstem. Immunohistochemical techniques will be used to identify discrete dopamine and norepinephrine subpopulations, which express AR and PR in the same cells. PR exists in two isoforms, PRA and PRB. Western blot analysis will be used to examine relative expression of PR isoforms in specific brain areas containing catecholaminergic neurons. Aim 2 is to assess interactions between progesterone and dihydrotestosterone (DHT) on TH mRNA levels in specific catecholaminergic neuronal groups. An in situ hybridization technique will be used to examine androgen and progesterone interactions to regulate TH gene expression in AR- and PR-containing catecholaminergic neurons. These studies will enhance our understanding of female reproductive functions and may have implications in non-reproductive functions modulated by catecholamine input. An increased understanding of the mechanism(s) involved in the interactions of these hormones can contribute to better health for women.